More new switched reluctance motor stuff

[reible]

This is from April 1998:

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So it has been around for a while. Someone with access to ASTM standards could more then likely find the original date without having to pay and it would be interesting to know how long some form of this has been around.

So while this went a different direction then expected perhaps it was worth the trip.

Ed

[garys]

Supposedly peak HP is the HP a motor would have when stalled out and burning up. Who cares? Just give me the running HP that it can deliver and get the job done. I don't care how much power the motor would have had when it stalled and burned up.

[dusty]

Peak HP is in reality that point where the device is generating more heat (ie: drawing more current) than the cooling system can compensate for. Back off and you save the motor.

Think variable speed routers.

[JPG]

Who what came up with THAT gobbly gook marketing 'information'.

Since one should rarely(hopefully) experience that 'developed' horsepower how is it relevant in typical everyday use?

Again a hypothetical instant in time. HP is time and distance related.

[dusty]

Compare apples to apples.

Compare vacuum cleaners (airwatts) to vacuum cleaners (airwatts).

Compare Dust Collectors (CFM) to Dust Collectors (CFM)

[BuckeyeDennis]

Who what came up with THAT gobbly gook marketing 'information'.

Since one should rarely(hopefully) experience that 'developed' horsepower how is it relevant in typical everyday use?

Again a hypothetical instant in time. HP is time and distance related.

I was also very skeptical of “developed horsepower” marketing claims, until one day I was contemplating an operation that required a lot of torque for a short period of time. Here’s where that train of thought led me.

As you know, the continuous rated horsepower of a motor tells us how much power the motor can make, forever, at a specified ambient temperature, without overheating. But home-shop woodworking operations hardly have a continuous load. Ripping an 8’ long hardwood board would be about as long as we would ever need maximum power, and even that is a very rare load condition.

Thermal time constants of decent-sized motors are usually measured in minutes, so actually overheating from a short-term load isn’t the issue. I just checked the specs for a 1 hp motor that I own. Safe time at stall is 10 seconds. Locked-rotor (stall) current is 21.4A. Continuous rated current is 3.8A. So resistive losses at stall current are (21.4/3.8)^2 = 31.7 times higher than under full continuous-load conditions — and the motor can handle that safely for ten seconds.

When operating in the usual speed/torque region, the operating point is “stable”. That is, if you increase the torque load, the speed will drop just a bit, and then the motor can happily supply the required torque. Until, that is, you hit the motor’s “pullout torque”, which is the highest point on the speed/torque curve. That’s the point of no return, because if the speed drops any farther, the available torque actually decreases, and the motor immediately stalls.

Now mind you, I’ve designed systems mostly with DC motors, and they develop peak torque at zero RPM. But an induction motor is a different animal. The speed/torque curve below tells the story.

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I don’t know this for a fact, but it seems logical that the “developed horsepower” numbers that the marketeers became so fond of are actually a specification of the horsepower available when operating very near the “pullout torque”. You can’t run there continuusly, for sure. But you probably could for upwards of a minute, which is ample for most woodworking cuts.

So in that sense, I do care about developed horsepower. The more I have, the heavier a cut I can take. And I’ll bet that I’d never trip the thermal overload unless I stall the motor, because I’m not doing continuous-production cutting.

[JPG]

Is that not relevant to induction motors?
My recollection(not a reliable thingie) is that developed HP seems to be something that is touted for universal motors.(???)

[BuckeyeDennis]

Is that not relevant to induction motors?
My recollection(not a reliable thingie) is that developed HP seems to be something that is touted for universal motors.(???)

I’ve mostly seen term ”developed horsepower” used for post-1960 radial arm saw marketing wars, and those had induction motors. Lord only knows what else it’s been used for. I’ve never seen a formal definition of the term. But with Google’s help, I just found the following “standard” from the Power Tool Institute.

https://www.powertoolinstitute.com/pti- ... erProc.pdf

Reading between the lines again, I still strongly suspect that the marketeers used the term “developed horsepower” synomously with “peak horsepower”. The PTI document is agnostic regarding the motor technology. To paraphrase the test procedure: “Put the danged thing on an honest dynomometer, and see how much power you can get without smoking it”.

[RFGuy]

Interesting discussion here, so I had to check out this "new" Shopvac. I believe the only model that I see for this is listed as more of a commercial/industrial model so that explains the $300 price tag, I think (unless "industrial" here is marketing BS). Switched-reluctance motor technology is definitely not new, but it is finding new applications as microcontrollers have become dirt cheap and the know-how of creating the driver electronics and control systems have proliferated to more companies. I found a few patents authored by Shopvac relating to switched reluctance motors. It looks like they have been researching this area for at least 15-20 years.

https://patents.justia.com/patent/8312590
https://patents.justia.com/patent/8286300
https://patents.justia.com/patent/20110234132

I always considered airwatts to be a marketing term. Yes it conveys some real world technical specs that reside underneath, but in the end it is hedged by the test conditions or whatever edge a manufacturer can eke out. The psychology of selling products to consumers always demands a bigger number on the box to differentiate their product from the competition. Airwatts serves this well...

A key benefit of switched reluctance motors, as I understand them, is they allow for a more powerful motor in a smaller footprint. Without this, it would be difficult to fit 2HP into the PowerPro headstock. In most motor applications, the motor tends to be over-designed to either allow for continuous operation and/or to have sufficient capacity for some peak load. By going with switched reluctance on a vacuum, I would think you could shrink the motor design, for a given power which means the lower end vacuums can be made more cheaply to improve profit margin. Given that the low end shop vacuums sell for around $50-60, there can't be much margin on these models so switching to switched reluctance and shrinking the motor while maintaining the same power could improve margins. Conversely going the other way on the high end shop vacs would equate to more power than the competition and the ability to charge more for the high end products.

https://www.shopvac.com/product/shop-va ... um:9241810

[JPG]

But it is 'supposed' to be NON-destructive.

“Put the danged thing on an honest dynomometer, and see how much power you can get without smoking it”.

Interesting language. Appears the writer has a suspicious bent.

Oh and it failed to define destructive.

All that just to be able to mislead!!!